The goal of this study is to determine the effect of postmenopausal hormone replacement therapy on cardiac function and plasma volumes and to determine if this effect is related to changes in serum renin, angiotensin II and aldosterone. This study proposes specifically to determine the effects of medroxyprogesterone acetate, 17 B-estradiol, and 17B-estradiol/medroxyprogesterone acetate on cardiac output, stroke volume, ejection fraction, left ventricular wall thickness and plasma volume in a whole body human model before and at certain time points on sequential hormone replacement therapy. Cardiac parameters will be determined by Doppler echocardiography, plasma volume by 125I-albumin dilution, and hormones by immunoassay. From 7/1/96-11/30/96, 12 of 18 patients were recruited for the four month study. Preliminary data show a 20-25% increase in cardiac output and stroke volume with estrogen plus progestin in one month. After four months, end systolic volume declines by approximately 20%, ejection fraction increases by about 10% and left ventricular mass increases by about 8% with 17B-estradiol or combined 17B-estradiol/ medroxyprogesterone acetate. In the last 6 months of the study, we anticipate recruitment will be complete and blood volume data will be available.